The round shape of a new species of fossil turtle found in Cerrejon coal mine in Colombia may have warmed readily in the sun. (Photo: Liz Bradford)

Paleontologists have uncovered a fossilized turtle shell of a newly discovered species that lived 60 million years ago.

Researchers from the Smithsonian Tropical Research Institute in Panama and colleagues at North Carolina State University and the Florida Museum of Natural History found the fossil in what is now northwestern South America and they report their findings the Journal of Paleontology.

The turtle is called Puentemys mushaisaensis because it was found in La Puente pit in Cerrejón Coal Mine, a place famous for other major discoveries, like that of the Carbonemys freshwater turtle that was as big as a smart car. The new turtle species is five feet long.

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All Cerrejon's fossil reptiles seem to be extremely large, reports TG Daily, and this latest discovery adds to the evidence that following the extinction of the dinosaurs, tropical reptiles were generally much bigger than they are now.

It wasn't just the size of Puentemys that stood out to researchers; one of its features set it apart from other turtle species.

"The shell was far more rounded than a typical turtle," lead researcher Carlos Jaramillo told LiveScience. It is about the size and shape of a large car tire said Edwin Cadena, a post-doctoral fellow at North Carolina State University.

The peculiar shape of the shell may have discouraged predators like the Titanoboa - the world's biggest snake - who would not have been able to open their jaws wide enough to engulf the turtle. The low-domed shape would also have helped regulate the cold-blooded turtle's temperature by increasing the area of the body exposed to the sun.

According to MSNBC, various factors, including plentiful food, fewer predators, large habitat and climate change, would have worked together to allow turtles and other animals to reach such relatively gargantuan sizes, scientists have suggested.